Class of service communication switching system



June 27, 1967 F, B, SMORSK. 3,328,535

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United States Patent O 3,328,535 CLASS OF SERVICE COMMUNICATION SWITCHING SYSTEM Frank B. Sikorski, Des Plaines, Ill., assignor to Automatic Electric Laboratories, Inc., Northlake, Ill., a corporation of Delaware Original application Aug. 27, 1963, Ser. No. 304,826. Divided and this application Dec. 1, 1966, Ser. No.

s Claims. (Cl. 179-18) ABSTRACT OF THE DISCLOSURE 'I'he disclosure relates to a switching network and marker used in a communication switching system. The network comprises a plurality of coordinate matrices with reed relay crosspoint switching devices. The marker is a combination of reed relays and electronic scanners for finding a path through the network and establishing a connection. The same network and marker are used for originating and terminating calls.

This is a division of my application Ser. No. 304,826 filed Aug. 27, 1963 and now abandoned. The drawings and the specification following the brief description of the drawings in the original application is identical to that of an application by W. R. Wedmore for a Marker For A Communication Switching Network, Ser. No. 804,892, filed Aug. 27, 1963, now Patent No. 3,293,368, which is made a part hereof as though fully set forth, and may be referred to for additional details of the system.

This invention relates to a communication switching marker selection arrangement, and more particularly to an arrangement for supplying the class of service of a calling line or trunk t-o common equipment.

U.S. Patent No. 3,170,041 by K. K. Spellnes describes a Communication Switching System having marker controlled crosspoint switching networks, and common control equipment comprising register-senders and translalators. Each register-sender group includes electronic apparatus shared on a time division multiplex basis, with a ferrite core array used in a recirculating arrangement. The system provides full translation on every call from the directory number to an equipment location number. Each subscriber in the exchange is identified to the other subscribers by the office code, or one of a number of office codes, of that exchange and by a line 'directory number. His line is also assigned in that exchange a particular appearance on a set of terminals of the switching equipment. This arrangement permits complete flexibility in the assignment of telephone numbers and terminals on the switching equipment, and eliminates the necessity for a line intermediate distributing frame. Any change of subscriber service is accomplished simply by changing the instructions stored in the translator. The translator preferably uses a magnetic drum. Changes on the drum are made simply by keying instructions in a control console. The translator equipment is arranged to be accessed from the register-sender groups. The translator assigns itself to a register at various times during dialing, for example at the end of a group of digits representing an office code or other special code.

The switching network comprises local subscriber line groups of 1000 lines each, selector groups, and incoming trunk groups. Each line group provides crosspoint switching matrices for `originating connections from calling local subscriber lines to originating junctors which are connected to selector inlets, and also through a register matrix to register junctors; and also provides matrices vfor terminating connections between terminating junctors Patented June 27, 1967 and called local subscriber lines, the terminating junctors being accessed directly from selector outlets. In the trunk group incoming trunks are connected directly to selector inlets, and also through a crosspoint switching network to register junctors.

On originating calls, both in the line group from local subscriber calling lines, and 4in the trunk group from incoming trunks, the marker during the establishment of the connection to a register after identifying the calling line or trunk for use in establishing the connection to the register, also transmits this line or trunk identification by high speed serial binary code to the register for storage. If ticketing is required the line number identification which has been received from the marker as an equipment location number is supplied to the translator to obtain the calling subscriber directory number.

According to the invention, class of service identification during the establishment of originating calls is obtained by providing an arrangement comprising a diode network connected between the pull (operate) conductors at the line terminals and a set of class of service conductors. After the calling line is identified and a route is selected to a register, the marker applies a class of service marking potential through the relay tree to the pull conductor at the line terminal, which potential is applied through the forward conducting direction of the diodes in series to one or more of the class of service conductors. These conductors are connected to a lsending arrangement along with identification conductors from the line identifier apparatus, and transmitted to the register for storage. The -relay tree for applying this class of service marking potential is the same relay tree which is subsequently vused to apply the operate marking potential to the pull conductor at the line terminal to establish a connection.

A switching network is covered by Patent No. 3,275,- 752 for a Communication Switching System, by M. H. Esperseth et al. A Patent No. 3,211,837 by L. Bruglemans covers a Line Identifier Arrangement for a Communications Switching System. The line identifier of the Bruglemans patent makes use of the switching network described in the Esperseth et al. patent, for identifying the calling line on originating calls. This line identifier includes the relay tree used to apply the marking potentials to the pull conductor at the line terminal. It is also used to supply the identification information which is sent with the class of service of the calling line to the register.

This system is arranged so that the same terminating junctors and switching network matrices which are used for ordinary terminating calls to local lines, are also used for special calls such as Wire chief or verification calls to local subscriber lines.

According to another feature `of the invention an arrangement is provided for disconnecting the potential (ground potential) which is supplied in common to the cutoff relay contacts. Thus during the special call if the marker finds the called line busy a device such as a fiipflop is set to record this fact, and the output thereof is used to cause the potential to be removed from the cutoff relay contacts so that the marker may complete the connection to that line.

The above-mentioned and other objects an-d features of this invention and the manner of attaining them will become more apparent, and the invention itself will be best understood, by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings comprising FIGS. l to 14 wherein: l '-Ii FIG. 1 comprises a block diagram of one line group for a telephone switching exchange showing a trunking diagram of the switching network, and a diagram of a marker;

FIG. 2 is a block diagram of the exchange;

FIGS. 3-6 comprise a schematic and block diagram of a line group and line group marker;

FIG. 7 is` a diagramyof a register-sender group, translator, and group selector;

FIGS. 8411 comprise a symbolic blo-ck diagram of the marker send-receive circuit;

FIG. 12 is a sequence flow chart;

FIG. 13 shows how FIGS. 3-7 are to be arranged;

FIG. 14 shows how FIGS. 8-11 are to be arranged;

FIG. 15 is a schematic drawing of the class--of-service and PBX marking units.

SYSTEM ORGANIZATION A system incorporating the invention is described in the following copending applications:

K. K. Spellnes, Communication Switching System, Ser. No. 230,887 tiled Oct. 16, 1962, now Patent No. 3,170,041;

M. H. Esperseth et al., Communication Switching System, Ser. No. 240,497 tiled Nov. 28, 1962, now Patent No. 3,275,752;

K. E. Prescher et al., Communication Switching System Common Control, Ser. No. 231,625 filed Oct. 19,r 1962, now Patent No. 3,173,994;

L. Bruglemans, Line Identifier Arrangement for a Communication Switching System, Ser. No. 231,425 filed Oct. 18, 1962, now Patent No. 3,211,837;

B. Sherstiuk, Sender for Communication Switching System, Ser. No. 280,053 filed May 13, 1963, now Patent No. 3,278,691.

Referring to FIG. 2, the system consists of the line group 100, group selector 300, `register-sender group 600, and the translator 700. There is also a trunk group 500 which provi-des access from incoming trunks to the registers, and a -control center 790 which contains a special computer for operation analysis and recording, and program upgrading equipment.

The signaling between the system groups is accomplished by a technique called -di-phase. This .method ernploys a phase shift technique for serial sending and receiving of pulses.

TRACING OF A LOCAL CALL As an introduction to the system operation, a brief description of a typical local call as processed through the system is now presented. The block diagram, FIG. 2, may be followed for tracing the call.

When a subscriber lifts the handset, the line group marker 200 goes into action iirst by detecting the originating call mark, identifying the callin-g line, and selecting an idle register junctor within the register-sender. A path is then temporarily established from the calling telephone to the register junctor via the A, B, C, and R matrices, and the subscriber receives dial tone. The dialed digits are stored temporarily, coded, and processing is continued as these digits are passed to the translator 700,

analyzed-for type of incoming call, and instructions are selected from the drum memory 730 and returned to the register-sender 600 to guide further handling of the call. Upon receipt of the remaining digits, the translator 700 returns switching instructions corresponding to the called number as store-d in the drum memory 730. 'The instructions are transmitted from the register-sender 600 via one of the senders 671-680 and the originating junctor 120 of the originating line group to the group selector 300. In the group selector 300, the instructions are analyzed by the marker 400, an idle terminating junctor 130 in the terminating line group is located, and a path established to that line group via A, B, and C matrices of the group selector. The remaining instructions are followed by the line group 4marker to locate the called line terminals, select and seize a path from the terminating junctor through the E, D, B and A matrices to the called line. The terminating junctor establishes ringing, answer supervision, and talking battery for both parties when the call is answered.

Since the systenris a common control operation, the markers of the line group and group selector function only to serve the assigned portion of the call processing then release to serve other calls. The register-sender 600 and the translator 700 are functioning on a time division basis and therefore are processing several calls simultaneously. The temporary signaling and control paths are released for further service while only the talking paths are held .through the switching matrices and junctors.

THE LINE GROUP Line group switching network A trunkinig. -diagram of one line group switching network is shown on the upper portion -of FIG. 1. The network is made up of coordinate crosspoint matrices. This section of the system may be thought of as a large switching unit capable of connecting any one of 1000` lines originating calls to any one of 120 circuits called originating junctors OJ. Likewise, this unit is capableof connecting any one of 120 circuits called terminating junctors T] and representing incoming calls to any one of the 1000 lines served -by this line group. Crosspoint matrices constitute the switching network and provide concentration going 4outward for originating calls, and expansion going inward for terminating calls. For practical and economic reasons, three stages A, B, and C, make up the outgoing switching stages. Four stages E, D,*B and A, make up the incoming switching stages. The 1000 subscriber lines divided into ten groups of weach,are located on the main distributing frame and from there are jumpered directly to the A stage. No line intermediate distributing frame is required. The A stage has 600 outlets or links (60 for each of the ten hundreds group) appearing as inlets -to the B stage. The B stage/,fin turn, has 300` links (30 -for each hundreds group) appearing as inlets to the C stage. The C stage has links to originating junctors. The originating junctors provide by-paths via the R stage to twenty-four registers and also provide access to the inlet circuits 310 of the group selector 300. Withthis switching configuration, a fully equipped line group is capable of handling a maximum traffic of three unit calls per line in each direction at a grade of service better than .01.

The switching stage matrices are made up Crosspoint reed relays, 15,000 for a fully equipped 1000` line group or 15 per line (12 per line for two unit calls per line). As shown in FIGS. 3 and 4, the reed relay coil has two windings, an operate (or pull) winding and a hold winding, and has three contacts. Two of the contacts switch the transmission loop. A third locks the hold winding to the sleeve or C lead.

The subscribers line equipment is similar to a conventional line and cut-olf circuit except that reed relays are used and fewer contacts are required. Reed relays were chosen over a static line circuit for simplicity and reliability of operation and for electrical isolation of electronic apparatus fr-om outside plant disturbances.

A maximum of thirty subscribers in agiven hundreds group may be engaged in different conversations at one time. One originating and one terminating junctor, two each of A and B Crosspoint reed relays, and one each of D, C, and E Crosspoint reed relays are held in the line group per conversation. Registers are held only during dialing.

The originating and terminating junctors mentioned earlier are reed relay circuits performing several functions. The originating junctor provides loop splitting facilities for an originating call. Initially, a transmission path is provided from the calling line to register and an additional path is provided from register to group selector for early outpulsing. When the called line is reached, the originating junctor switches the calling line through to the terminating junctor via the group selector. The circuit also provides a busy tone bridge in the event ofno link availability.

The terminating junctor performs functions necessary to extend the call to a called subscriber. It provides a path into the line group marker for signaling between the code receiver in the marker and the sender circuit. The circuit provides regular or party line ringing controls, ring back tone, and ring cut-off controls. When line busy is encountered, busy tone is provided at this point. It provides transmission battery feed for both called and calling parties. On test calls and busy verification calls, the junctor removes the battery feeds and switches the calling line metallically through to the called line. For oicial calls, answer superivsion is disabled within the junctor to prevent charging of the calling end. Thus, it is seen that special service calls are also handled :by the terminating junctor via the regular switching network eliminating the need for a special switch train.

Line group marker Two markers 200 are always provided and the 1000 line groups are divided between the two up to a maximum of five line groups per marker. Each marker serves its associated line group matrices on an allotted basis, but, is also capable of assuming the load of its companion marker.

In its idle state, a marker continuously scans for requests for service from the line groups with which it is associated. Upon recognizing a call, either originating or terminating, in a particular line group, it locks out all other rgr-oups via its allotter and allows the connect circuitry of the selected group to switch in the matrix leads into the marker for processing. Approximately 400 leads are so controlled. All calls in the allotted line group are processed before the marker returns to its idle state to serve other groups.

When connected to a line group, the marker has two primary functions, connect a line originating a call through the matrices and originating junctor to a register and to connect a terminating junctor (representing an incoming call) through the matrices to the called line. Both reed relays and electronic circuitry are used to perform these jobs. The electronic circuitry provides all logic and scanning operations requiring high speed. Reed relays are used merely for connecting purposes, to switch in the necessary groups of leads into the electronic circuitry for analysis. With this combination of components, the processing of a request for service by the line group marker is accomplished in approximately 100 milliseconds.

For each function, the marker performs several tasks. In general, for originating traffic, it must provide line number identification, pathfin-ding and route selection,

lsending of line number identification, class of service, and

line group identity, For terminating traffic, it must provide terminating junctor identification, transceiver for communicating with the sender circuit, access to called line for busy test, PBX selection, and pathfinding and route selection.

The tasks performed by the marker in processing a call are controlled by a sequence and supervisory circuit 290. This control may be compared to a programmed computer in that the marker follows a fixed plan of operation.

All marker operations are governed by this control.

Included in unit 290 is the clock circuit which provides pulses to synchronize operations within the marker and the timing circuitry which is used to generate various timeout periods such as that provided between a reed relay operation and a succeeding electronic scanning operation. Once the supervisory control recognizes a request for service, either terminating or originating, it will process this call from beginning to end, locking out all other calls.

A two-way communication path exists between the marker processing a terminating call and the sender circuit. In addition to receiving the called line number and any special instructions regarding the line, the marker may signal back to the sender any conditions peculiar to the line such as line busy, line idle, link congestion, recycle and send again, and be referred back to the sender for appropriate action.

If on a terminating call, the marker transceiver received i a PBX call indication, a PBX selector circuit marks all THE GROUP SELECTOR Group selector matrix The intermediate switching functions of the system are performed by a group selector 300, FIGS. 2 and 7. Three stages of crosspoint switches are provided. The first switching stage 312, the A stage, contains 60 cards of 50 crosspoints, each arranged in a 5 X 10 matrix. This switching matrix is associated with the inlet circuit 310 line and cut-off reed relays to the group selector. The second switching stage 314, the B stage, contains 60 cards of 60 crosspoints each in a l0I x 6 matrix. The third stage 316, the C stage, uses a basic arrangement of 60 crosspoints in a 6 X 10 matrix to provide 600 outlets. The group selector has 300 inlets 310 serving the originating junctors in the line groups and incoming trunks.

The outlets of the group selector are arranged as 120 levels of l0 trunks each. These levels may be combined to accommodate trunk groups of any size.

Group selector marker The operation of the group selector is controlled by an electronic marker 400. The marker has control of all crosspoints in the group selector and sets up calls on a one-at-a-time basis. The marker operates in response to selection digits received electronically in its transceiver 480 from the register-sender group. The holding time of the marker is approximately milliseconds.

Operational description In its idle state, the group selector marker is continuously scanning the group selector matrices for new calls. The register-sender group, via an originating junctor or incoming trunk, initiates a demand on a group selector by pulling the inlet line reed relay. When associated with a matrix, the marker finding the inlet demanding service stops its scanning at that point and connects a transceiver to the demanding inlet. The routing digits are sent in high speed code from the sender into the marker transceiver. During this same time, the marker operates connect reed relays to de-termine the link availability from the demanding inlet in the A stage toward the outlets through the B and C stages. Two routing digits are received by the transceiver in the marker and extende-d -to the trunk selection portion of the marker where connect reed relays gate lidle test leads of the selected trunk group into the trunk scanning portion. Within this scanner the link availability is combined with the trunk idle leads such that an idle trunk can appear idle to the scanner only if an appropriate idle link to the inlet exists.

If the trunk scanner inds an idle trunk, it pul-ls the proper group selector crosspoints, checks to make sure that the selected trunk becomes busy indicating seizure through the .group selector crosspoints, and clears its circuits.

THE TRUNK GROUP Trunk group matrix The trunk group '500 (FIG. 2) provides access for incoming trunks from outside of the office or for special intra-oliice trunks such as operator or wire chief. A trunk group m-atrix is capable of connecting any one of 75 incoming ltrunks to any one of sixteen registers on a single output level basis.

7 Trunk group marker The operation of the trunk group matrix is controlled by an electronic ,marker 550 which has control of all reed relays and sets up connections on a one-at-a-time basis. The marker operates in response, to a call for service from a trunk group and sets up a path based o-n information concerning the condition of a register junctor (busy or idle) and the condition of any link (busy or idle). The holding time vof the marker is approximately 50 milliseconds which is well within the interdigital switching time of any direct controlled system.

THE REGISTER-SENDER The register-sender .group 600 (FIGS. 2 and 7) is a time shared, common control -unit with the ability to register and process twenty-four simultaneous calls. The fully equipped unit -consists of twenty-four registers and ten senders.

The registers operate in a time division mode. There is one register junctor for every register in the group. Real time to time division entry is provided bythis circuit. A common control unit 664 comprises time rdivided circuits which are shared by all twenty-four registers. These circuits are used by each re-gister in turn and are organized to prov-ide the need registrationvand process control for `the registers. A temporary storage facility 660V is provided for the register grou-p. Each register has an assigned storage area wherein all register information is placed to allow time division operation by the common control. A folded Word oriente-d ferrite core memory is used for this purpose.

The extension of the proper switching digits, to the line or trunkselection stages of the system and to other connecting exchanges, is accomplished with a group of ten senders l671-680. These senders operate under the control of the registers and are used to transmit information in a dial pulse, multiefrequency, or code pulse manner.

Communication with the system translators, line group markers, trunk markers, and group selector markers is accomplished by high speed serial transfer of digital information using di-phase.

Circuit description In order to facilitate understanding .the following brief description of each of the circuits Within the registersender group is given.

The primary function vof the register jun-ctors 601-624 is to provide a buffer between the electronic equipment and the outside plant facilities. As such, the circuit employs reed relays for all switching functions,l performing all -those functions that require direct connection to the calling line or trunk. These include dial pulse repeating, dial tone control, battery feed for the calling line or trunk, calling station identification on party lines, test for coin deposit, coin refund, and test for coin refund. The circuit also controls the switch train and provides for peg count and traffic metering. Both multi-frequency and dial pulse juncto-rs are used.

The sende-r circuits 671-680 provide means for transferring information (dialed digits or switching instruction) over the voice transmission path from the registersender to the office markers or to distant offices. The sender is -a universal sender inasmuch as it provides all modes of sending required by the system. Di-phase send- -ing is employed for transmission of switching instructions to the office markers. The .di-phase part of the circuit Iis actually a transceiver 5400 since it provides `a means of 4receiving instructions from the markers as well as sending to the markers.

For outgoing cal-ls, the sender provides for both dial pulse and multi-frequency signaling. The circuit operate-s in conjunction with the sender controller 670 which is common to all senders in the register-sender group. The sender controller supplies the sender with the digits to be 8 sent out and indicates the mode of sending to be employed.

The sender circuit Iis mainly an electronic circuit except for outgoing vloop supervisory equipment where reed relays are used.

The register receiver 630 is seized by the register controller 664 and assigned t-o serve the register junctor on a hold-til-finished basis. The circuit receives either the line number identification generated by the line markers or the trunk number identification gene-rated by the trunk markers. On seizure of the circuit, 4a di-phase link is established t-o the marker being served. When all the digits have arrived in the :register receiver, the information is presented .to the register controller for storage in the area of the ferrite c-ore array 660 associated with the register being served. Upon completion of this storage process, the register receiver 630ais released for use by the next register requiring service.v

The register contr-oller 664, operating on a time division multiplex basi-s, controls the progress of each callv being processed. Within a particular time slot, this circuit up-dates the information in storage in the section of tthe core array associated with the time slot register.

The register transceiver 690 operates as the communication device for information transfer between the register-sender group and the system translators. It, like the register receiver, operates on a hold-until-finished basis. This circuit provides two-way di-phase serial communication between the translators and the register-sender group.

The organization of this circuit is such that the transfer of information from the read-shift buffer t-o the register controller is in 'a parallel manner. Seizure is dependent on the condition of .the control information available in the carry buffer.

The sender controller 670 utilizing information available to it in the read-shift buffer, controls the yflow of l information to be sent by thesender in use. It forwards control signals tothe proper senders such as mode of send signals, end of send signals, and release signals. It

present-s to the senders Ithe appropriate switching, and

if necessary, dialed digits for proper routing of the subscribers call.

The sender assigner 683, on request of the register controller, will connect an idle sender to the register junctor requiring service. The connection established by the assigner in the beginning of the terminating switchtrain, which will be extended by the system switching stages on informationreceived from the sender. The sender assigner operates on a hold-til-finished basis.

THE TRANSLATOR The translators 700 of the system provide semipermanent storage used by the system to direct the extension of telephone calls in accordance with the subscriber dialed digits.

lInform-ation storage is providedby magnetic drums 730 on the basis of one drum per translator. Memory words are recorded on the drum surface for a supervisory console 790, by simply typing the memory Word and yappropriate memory address at the console typewriter. This directory number an-d/or code translation can be added or exist-ing translations `altered with a minimum of maintenance effort.

LINE GROUP AND MARKER-DETAILED DESCRIPTION FIGS. 3-6 when arranged -as shown in FIG. 13 cornprise a schematic and block diagram of -a line group and line group marker. The line group and marker are also shown in F-IG. 1. The line circuits, switching matrices, and junctors are shown in FIGS. 3 and 4. The line group connect circuit 148 land the marker 200 are shown in FIGS. '5 and 6. The send receive circuit 280 is shown in more detail in FIGS. 8-11, arranged as shown in FIG. 14.

FIG. 1 shows the arrangement and interconnection of the switching matrices and junctors in a line group.

The subscriber lines are connected on the horizontal inputs of the A matrices, such that ten lines are connected at each A matrix. Therefore ten A matrices are provided for a group of 100 lines. Also for each hundreds group, six 1B matrices are provided, each B matrix having one input connected to each A matrix. Common to the ten hundreds groups or one thousand Ilines of a line group, there are thirty C matrices, and thirty corresponding D matrices. The connections are such that each C matrix and its corresponding D matrix has its ten inputs connected to the ten diierent hundreds groups. The Verticals of the C matrices are connected to respective originating junctors, with originating junctors 011-0130 connected to the respective first verticals of the Cmatrices, -originating junctors 0131-0160 connected to the second verticals of the respective C matrices, originating junctors 0161-0190 connected to the third verticals of the respective C matrices, `and originating junctors 0191- 01120 connected respectively to the fourth verticals of the C matrices.

The originating junctors each have one output connection -to the IDF for connection to the inlets of the group selectors, and another connection to the vR matrices. Originating junctors 1-20 lare connected to the respective horizontals of matrix R1, originating junctors 0121-0140 are connected to the horizontals of the matrix R2, c-ontinuing up to matrix R6 which has its horizontals connected to originating junctors 01101-01120. There are four vertical links from each R matrix, or a total of twenty-four, which are connected to the IDF for connection lto the register junctors in the register sender group 600. The register junctors in each register sender group are connected to the R matrix vertical's of several dilerent line groups.

The E matrices each have twenty horizontal links connected respectively to twenty different D matrices, with matrix E1 connected to rst Verticals of matrices D1-D20, matrix E3 having its first ten horizontals connected to rst verticals of matrices D21-D30 and its second ten horizontals connected to second verticals of matrices D1- D10. Matrix E3 has its twenty horizontals connected to second verticals of matrices D11-D30. Matrices E4 to E8 are similarly connected to other links of the D matrices. The verticals of the E matrices, fteen from each matrix, are connected to the terminating junctors.

All of the matrices are designated by reference characters in which an initial letter designates the switching stage. In the A and B stages the letter is followed by two numbers. The rst number indicating the hundreds group and the second letter indicating the matrix Within the hundreds group. Thus in hundreds group one there are ten A matrices A11-A10 and six B matrices B11-B16. These A and B stages are interconnected by links designated by the letters AB followed by three numbers, in which the tirst number indicates the hundreds group; the second number indicates the A matrix in the hundreds group and the third number indicates the B matrix in the hundreds group to which the link is connected. Thus link AB111 of the first hundreds group connects card A11 to card B11. The lines from the line circuits to the inputs of the A stage are designated by the letter L followed by three digits, with the tirst number indicating the hundreds group, the second number indicating the A matrix within the hundreds group and the third number indicating the input of the A matrix. Thus lines L111- L110 are connected to the ten inputs of matrix card A11. In the C stage the matrix cards are designated C1-C30, and in the D stage the corresponding D matrices are designated D1-D30. The links interconnecting the B stages to the C and D stages are designated by the letters BC followed by three numbers. The rst number indicates the hundreds group of the B matrix and the last two numbers indicate the C and D matrix, with a zero 10 inserted as the center number for connections to cards C1-C9 and D1-D9.

The links interconnecting the D and E stages are designated by the letters DE followed by three numbers. The rst number indicating the D matrix with a zero preceding the matrix number for the matrices D1-D9, and the last number indicating the D matrix.

The schematic diagrams of FIGS. 3 and 4 show one or two crosspoint reed relays of matrix cards of these stages; and also a line circuit, an originating junctor and a terminating junctor. Each link comprises four conductors, tip T, ring R, control C, and pull P. The tip and ring conductors provide an extension of the subscribers loop for a talking path, the pull conductor is used to operate the crosspoints, and the control conductor is used to hold the crosspoints in a selected path. Between each horizontal link and each vertical link of a matrix card there is a crosspoint switch comprising three make contacts in three capsules, two windings, and a diode. To establish an originating path after the marker has selected the route, an operate circuit is established on the .pull conductor through the three stages in series, through one crosspoint switch in each stage, to operate the crosspoints, then a hold path is established on the C conductor through the three crosspoints to hold the connections.

The line circuit LC111 comprises a line relay 12L having two windings and a single make contact, and a cuto relay 12CO having a winding, two break contacts and a make Contact. The tip and ring conductors of line L111, which are connected to the subscribers loop, are also connected via the break contacts of the cuto relay 12CO through the windings of the line relay 12L to ground and negative battery respectively. The conductor L111C is connected through the winding of the cutoff relay 12CO to negative battery. The conductor L111P is connected through the make contact of relay 12L and a resistor 1211 to conductor LR1 tothe marker; and also through the make contacts of the cutoff relay 12CO and a diode 1212 to conductor BCO to the marker. The conductors LRl and BCO are multipled to all of the One thousand line circuits of the group. There is also a connection from the cutoi relay by an individual conductor WC111 to the marker, for wire chief use.

The originating junctor (FIG. 4) provides connections from the originating path from the C matrices by a line 011A through the junctor and line 011B and the R matrix to a register junctor, and line 011C to the IDF for access to an inlet circuitof the group selector. The transmission path (conductors T and R) from the C matrix to the group selector is split in the originating junctor. The incoming path is connected to the register by leads TR and RR; and the outgoing path by conductors TS and RS to the sender. The contacts of relay 151B provide the split. Switching through of the connection from line 011A to line 011C is accomplished by operating relay 151B under control of the register via lead ECR, which in turn causes the operation of relay 151A.

Holding of the preceding switch train by ground on the lead C of line 011A is under control of the register junctor via lead CR to relay 151A before cut through; and under control of the group selector via lead C in line 011C to relay 151A after cut through. The R matrix is released after cut through.

If a link busy condition is encountered, relay 15BT is operated by the register junctor via lead BY to return link busy tone i.p.m.). Relay 15BT remains operated under control of the calling group. No cut through occurs under this condition.

The terminating junctor (FIG. 4) provides access from a group selector outlet, via the IDF and line T11A through the junctor to line TJlB and thence through matrices E, D, B and A to a called line.

Battery feed is provided to the calling line by relay 18BF, and to the called line by relay 17BF.

Busy-idle indication is provided on lead IT of line TJ 1A for use by a parallel test circuit in the group selector marker.

Relay 17TIS when operated provides a path from the TO and RO conductors of line Tl 1A to conductors TC and RC of line T IC, which completes a path from the sender over the transmission path to the send receive circuit in the marker. This'relay is operated under the control of the marker by a signal on lead TJ. Relay 17TI S also completes a path for the ringing code signals from the send receive circuit on conductors A, B, C and D of line TJCto the ringing control relays (not shown).

The junctor is seized by ground forwarded via lead ECO of line TJ 1A to operate relay 17S. This relay cornpletes a path to ground to hold the preceding switch train, and another path to ground to hold the succeeding switch train.

Operation of one or more of the ringing relays (not shown) applies one of ve different ringing frequencies to either lead T or lead R to provide fully selective liveparty bridged or ten-party divided ringing, in accordance with the binary code received on leads A, B, C and D as shown in the following table.

A B C D Gen. Connection Ringing Frequency 0 1 1 O T F4 0 0 O 1 T F5 0 X 1 1 T F1 SPECIAL FUNCTIONS 1 1 0 1 Return line busy (60 i.p.m.)

0 X 1 1 No ans. supy. (19OFC operates) 1 Xv 1 1 No ans. supy. or ringing (19 OFC and rnetallic eut-through (1931)() operates) Ringback tone is supplied to the calling party during ringing. Busy tone from a 60l i.p.m. source is supplied to the calling partyrwhen the proper binary code as shown in the table is received from the marker to operate a busy relay (not shown).

In response to answer supervision a ring trip relay (not shown) operates and shorts the -winding of a relay (contacts only shown) which connects the called party to the voice transmission path. Relay .17BFthen operates, and applies ground which extends through break contacts of relay 190FC (contacts only shown) to lead ECO of line TJ 1A to repeat answer supervision to the preceding switch train.

In response to one of the codes as shown in the table, relays 19SPC and 190FC operate to provide a metallic path (T and R) free of attachments and inhibits ringing and answer supervision for verification, wire chief, and routiner calls. In response to another code, relay 190FC operates to inhibit answer supervision on calls vto official numbers, such as the telephone company business oice.

Release of the succeeding switch train may be controlled by a routiner. Opening lead EC relases the succeeding switch train but holds the terminating junctor seized. The terminating junctor is released when negative battery potential is applied to lead EC.

Release of the preceding switch train is delayed approximately 135 milliseconds after the calling party re-l leases to protect against unintentional interruption of the calling loop.

Timed disconnect of the preceding switch train and the terminating junctor 3G seconds after the called party disconnects is provided.

An arrangement is provided to permit the called party 12 to hold the succeeding switch train and the terminating junctor.

The line group connect circuit 148 is shown by triangles and trapezoids representing relay treesin FIGS. 3 and 4, and also in FIG. 1. The line group marker 200 isy shown by a schematic and block diagram in FIGS. 5 and 6, and also by blocks at the bottom of FIG. 1. For convenience in the drawing, relays are shown having a large number of contacts although in the physical embodiment of this system the reed relay assemblies have been limited to ten contacts, and additional contacts are obtained by using parallel andslave connected reed relays. A relay driver device shown symbolically in the drawings by a triangle with a line across it and associated make contact, comprises a single transistor amplier with a winding in its collector circuit and the single contact which is a reed capsule operated bythe winding.

The principal units of the line identiier are a hundreds scanner 2903, a tens scanner 2902, and a units scanner 2901. These units may be scanners or parallel test and control of pulse sources and sequence state circuits in the sequence and supervisory unit 290 have been used. The output devices comprise relay drivers 2931-2940 from hundreds scanner 2903, relay drivers 29151-29301 from tens scanner 2902, and relay drivers 2811-2820 from units scanner 2901. The relays which are operated under the control of the relay drivers are relays HIJ-I0 associated with the hundreds scanner-29013, relays Tf1-T0 associated with the tens scanner 2902, and relays U1U0 associated with the units scanner 2901.

Looking at the P leads of the horizontal inputs of a i single one of the matrices such as matrix C1,l a negative potential applied to the P lead in any one of the line circuits can be detected through the diodes and pull windings of the A and B matrix cards, since the diodes are forward biased. Thus a negative potential applied to the P lead at any line circuit of hundreds group 1 such as to conductor L111P, can be detected at the rst horizontal input of matrix C1, on conductor BC101P. Likewise a call in any of the other hundreds, group of the G-line group will appear at a corresponding one of the P leads of the horizontal inputs of matrix C1. These. leads are taken through contacts of relay HE, to the ten inputs of hundreds scanner 2903-. Likewise in each hundreds group the P leads of the horizontal inputs of any one of the matricescan detect a potential at any one of they ten lines of the A matrix card connected to that input. Thus in hundreds group 1 a call at any one of the lines L111 to L at the inputs of card A11 will appear at the conductor AB111P at the input of card B11. The ten leads AB111P to AB10'1P from card B11 of hundreds group AB1 (FIG. 1) and the corresponding ten leads from matrix card B11 of each of the other hundreds groups are taken through relay tree HEP which selects the ten leads of one hundreds group in accordance with the output of the hundreds scanner, and the ten leads are then taken through contacts of relay HE to the ten inputs of the tens scanner 2902. At the horizontal `input terminals of the A cards, all of the 100011J leads, ten from each card of the 100 A matrix cards7 for example, leads L111P to L110P of card A11 of group AB1, pass through relay tree LS which selects the ten leads from one A matrix in accordance with the hundreds and tens selection, which are taken through contacts of relay LG and contacts of relay UP to the units scanner 2901. The inputs to each of the scanners are multipled to the other line groups as shown by the multiple symbols.

Sequence and Supervisory Circuits 290 The sequence and supervisory circuits 290l include a sequence state register, miscellaneous Hip-flops, an operational timer, and a cycle counter, which supply signals used by the other units in the marker. These ciruits will be referred to in the section describing the operation of the marker.

The sequence state flow chart is shown in FIG. 12. On the ow chart each of the boxes includes the decoded designation of the sequence state at the top and below it yappears the binary code of five nip-flops representing that sequence state. The significance of each of the sequence states is explained in the section on operation of the line group marker. Briefly, states S2-S13 are for originating calls, states S14-S28 for terminating calls and states S29 and S30 are idle states. At the end of each call sequence state S29 is entered, and if there is another call in the same line group state S1 is entered. If there is no call in the same line group the sequence changes from S29 to S30, and if the allotter shows a call in another line group the sequence goes from S30 to S29 to S1. If there is a terminating call it is given preference and state S14 is entered. If there is an originating call and no terminating call state S2 is entered.

Send-receive circuit 280 Referring now to FIGS. 8-11, the line group marker send-receive circuit 280 provides a means to communicate with other sections of the system via high speed serial transmission. The send-receive circuit comprises an LNI sender for originating calls, a terminating call portion, and a common transceiver. The LNI sender 4000 is shown in FIG. 8 as comprising an LNI shift register 4011, an LNI encoder 4010 for parallel loading of the shift register, and logic circuit 4012. The terminating call portion comprises a shift register shown by functional blocks extending across the bottom of FIGS. 8 and 9, along with logic circuits in FIGS. 10 and 11. The common transceiver 4100 is shown in FIG. 9, and comprises a receiver 4105, synchronizing circuits 4106, a transmitter 4107, and control circuits.

The LNI portion of the send-receive circuit is provided to transmit the hundreds, tens, units, class of service, and line group matrix identity of the originating line information to the register sender group. This information is parallel loaded via the LNI encoder 4010 into the LNI shift register 4011. 'Ihe relay driver 4101 closes its contact between resistance battery and the winding of relay 41LNI to thereby transmit a signal over lead BY,

and as shown in FIGS. 6, 4 and 7, through the relay tree RG to the register junctor 601. This signal is repeated via circuits in the register junctor 601 and lead multiplex 624 to the register, which provides an acknowledgment by operation of relay driver 5323 to put an additional ground via relay GO on lead BY, which causes relay 41LNI to operate. The information from the shift register 4011 is then transmitted serially using transmitter 4107, through contacts 41LNI41 and 41LNI2 to conductors TR and RR and transmitted through the register junctor 601 into register receiver 630.

The terminating call shift register comprises ip-op SU1, four flip-ops HU1-HU4 in FIG. 8, flip-flops TP1 TP4, iiip-flop PR1, flip-flop BFI, and flip-flop BF2 in FIG. 9. Di-phase control circuits and various logic circuits for terminating calls are shown in FIG. 10, and decoder circuits associated with the terminating call shift register are shown in IFIG` 11. Logic is provided for loading and sending instructions (i.e. trunk busy, resend, incomplete, etc.) to the register sender group. Logic is also provided for checking parity of the received data (even number of binary ones received), which is accomplished by flipops TM1 and PR2. These two flip-Hops are used for both the originating shift register and the terminating shift register. Logic is also provided to clear and load data into the shift register.

The code conversion for the terminating portion of the `send-receive circuit provides logic to store the information received in the terminating shift register and to change the stored binary information into decimal form for use by the other line group marker circuits. This data constitutes the equipment location identity of a line or PBX group to which the call will be terminated and comprises the hundreds decoder HT, tens decoder TT, units decoder UT, and the party digits and wire chief decoder. Special instructions such as verilication and wire chief are processed as part of the party digit information. Decoders PH, PT, and PU generate the PBX information. Logic AND gate 4207 generates the connect signal which is sent to the sender when the transmission path is established thereto. Logic AND gate 4210 generates the incomplete or resend command which is decoded by the sender transmitter in the register sender group. Trunk busy, line busy, and line idle are generated by the sequence and supervisory circuit. Logic AND gate 4214 generates signal DZ which indicates all zeros in the shift register. Logic AND gates 4238 and 4229 generate command ZR which is used by the sequence and supervisory circuit.

OPERATION OF LINE GROUP MARKER-ORIGI- NATING CALL The operational description may be followed on FIGS. 3-7, or FIG. l may be used in place of FIGS. 3-6 with FIG. 7, or FIG. 2 may be used.

Assume now that the subscriber at station S111 initiates a call. In response to the closing of the subscriber loop, the line relay 12L of line circuit LC111 operates and closes its contacts. Negative battery potential through the break contacts of relay LR is applied over conductor'LRl and resistor 1211 of line circuit LC111 and the contacts of relay 12L to the pull conductor L111P, thence through diodes and pull windings on card A11, and card B11, to

conductor BC101P at the input of card C1. The potential is also applied through a diode and pull winding of card C1 to the lead OJlAP of vertical V1, thence by way of conductor OC to an input of the allotter 252. The allotter operates relay LG, and other line groups are locked out. The supervisory signal HF through `contacts of relay LG operates relay HE. Relay HE prepares operate circuits for the relay tree, connects through the conductors BC101P to BC001P to the hundreds scanner 2903.

Referring now to the flow chart, FIG. 12, and assuming that the marker was in the idle state S30, in response to signals LG and OC from the allotter, the sequence operation is started, going from S30 to S29 to S1.

It is assumed that there is no terminating call, so the marker goes to the originating call sequence, entering S2. The marker determines whether there is a call in the priority hundreds group 1. If the call is in other than hundreds group "1, a signal OCX is generated and steps y the sequence to state S3, which causes a 10-step counter in the hundreds scanner 2903 to start and step until it finds coincidence of its output with a signal at one of the inputs to the scanner. The scanner then operates the corresponding one of the relay drivers 2931 to 2940, which places ground on lead HX-0.

However in ou-r case the call is in hundreds "1, which is given priority, so a signal OC1 is generated, and the sequence goes to state S4.

The signal S4 causes hundreds scanner 2903 to directly operate the relay driver 2931 which supplies ground potential to operate the relay H1. Relay H1 locks to ground potential at break contacts of relay LKM. Ground potential through contacts of relay H1 completes the operating path for relay tree HEP, connecting conductors AB111P to AB101P from card B11 via contacts of relay HE to the inputs of the tens scanner 2902. A ground signal at contacts of relay H1 is transmitted by way of 

1. IN A COMMUNICATION SWITCHING SYSTEM HAVING A SWITCHING NETWORK FOR ESTABLISHING CONNECTIONS BETWEEN ANY ONE OF A PLURALITY OF LINE CIRCUITS CONNECTED TO A LINE SIDE OF THE NETWORK AND ANY ONE OF A PLURALITY OF ORIGINATING TERMINALS ON THE OTHER SIDE OF THE NETWORK, CONTROL MEANS WHICH RESPONSIVE TO A CALL-REQUEST SIGNAL CONDITION AT ONE OF SAID LINE CIRCUITS CONTROLS THE FINDING OF A PATH AND THE ESTABLISHMENT OF A CONNECTION THROUGH SAID NETWORK FROM SAID LINE CIRCUIT TO ONE OF THE ORIGINATING TERMINALS; 